Pass task runners to AudioManager constructor.

media/audio/audio_manager.h

Index: media/audio/audio_manager.h
diff --git a/media/audio/audio_manager.h b/media/audio/audio_manager.h
index d3eea4a6b9cdcf5b944e076dc12e983a82109b05..8018d68ab024fb64822b5b2373484835165f4325 100644
--- a/media/audio/audio_manager.h
+++ b/media/audio/audio_manager.h
@@ -49,18 +49,25 @@ class MEDIA_EXPORT AudioManager {
   // Construct the audio manager; only one instance is allowed.  The manager
   // will forward CreateAudioLog() calls to the provided AudioLogFactory; as
   // such |audio_log_factory| must outlive the AudioManager.
+  // DO NOT DELETE the returned instance. Use AudioManager::Destroy.
   static AudioManager* Create(AudioLogFactory* audio_log_factory);

[DaleCurtis, 2016/03/18 00:19:10]

Hmm, I thought you were changing this to Create(..., |task_runner|)? Then you
can just say that AudioManager must be deleted on |task_runner|.

[alokp, 2016/03/18 00:35:19]

I wanted to keep task_runner an internal detail of AudioManager implementation.
As a client of AudioManager I do not care which task_runner is used. I should be
able to just call AudioManager::Create and rely on the platform implementation
to choose an appropriate thread.

Otherwise how do you propose BrowserMainLoop get a task_runner to pass into
AudioManager::Create?

We could add a static AudioManager::GetRecommendedTaskRunner to be implemented
by various platforms. Is this what you had in mind?

[DaleCurtis, 2016/03/18 00:40:41]

No, I was expecting that you would require the task runner to be passed in
always or at the very least that you'd have one method which took no task runner
and used a default and a second which allowed one to be passed in.
Alternatively, BML would have it's own base::Thread it starts and passes the
task runner in for on non-OSX, non-Cast platforms.

This would help both your use case and our test situation immensely since we
have a ton of tests which have to hop to the platform default thread instead of
just using a test task runner.

[alokp, 2016/03/18 06:46:52]

I was under the impression that those tests were intentionally written that way
to test AM in multi-threaded environment :D

Passing the task runners into Create SGTM. PTAL at the latest patch that
combines the various Create functions into one and also passes the task runners.
The task runners are optional to allow the platform to choose a default one if
not specified.

It should be now trivial to update those tests to use a test task runner. I can
do that in follow-up patch.

 
   // Similar to Create() except also schedules a monitor on the given task
   // runner to ensure the audio thread is not stuck for more than 60 seconds; if
   // a hang is detected, the process will be crashed.  See EnableHangMonitor().
+  // DO NOT DELETE the returned instance. Use AudioManager::Destroy.
   static AudioManager* CreateWithHangTimer(
       AudioLogFactory* audio_log_factory,
       const scoped_refptr<base::SingleThreadTaskRunner>& monitor_task_runner);
 
   // Similar to Create() except uses a FakeAudioLogFactory for testing.
+  // DO NOT DELETE the returned instance. Use AudioManager::Destroy.
   static AudioManager* CreateForTesting();
 
+  // Helper function to ensure that AudioManager is properly shutdown
+  // and destroyed on the audio thread.
+  static void Destroy(AudioManager* instance);
+
   // Enables non-crash dumps when audio thread hangs are detected.
   // TODO(dalecurtis): There are no callers to this function at present. A list
   // of bad drivers has been given to Microsoft. This should be re-enabled in
@@ -178,12 +185,18 @@ class MEDIA_EXPORT AudioManager {
       const std::string& device_id) = 0;
 
   // Returns the task runner used for audio IO.
-  virtual scoped_refptr<base::SingleThreadTaskRunner> GetTaskRunner() = 0;
+  // TODO(alokp): Rename to task_runner().
+  scoped_refptr<base::SingleThreadTaskRunner> GetTaskRunner() const {
+    return task_runner_;
+  }
 
   // Heavyweight tasks should use GetWorkerTaskRunner() instead of
   // GetTaskRunner(). On most platforms they are the same, but some share the
   // UI loop with the audio IO loop.
-  virtual scoped_refptr<base::SingleThreadTaskRunner> GetWorkerTaskRunner() = 0;
+  // TODO(alokp): Rename to worker_task_runner().
+  scoped_refptr<base::SingleThreadTaskRunner> GetWorkerTaskRunner() const {
+    return worker_task_runner_;
+  }
 
   // Allows clients to listen for device state changes; e.g. preferred sample
   // rate or channel layout changes.  The typical response to receiving this
@@ -230,9 +243,13 @@ class MEDIA_EXPORT AudioManager {
       AudioLogFactory::AudioComponent component) = 0;
 
  protected:
-  AudioManager();
+  AudioManager(
+      const scoped_refptr<base::SingleThreadTaskRunner>& task_runner,
+      const scoped_refptr<base::SingleThreadTaskRunner>& worker_task_runner);
 
  private:
+  scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
+  scoped_refptr<base::SingleThreadTaskRunner> worker_task_runner_;
   DISALLOW_COPY_AND_ASSIGN(AudioManager);
 };